Cytotoxic T lymphocyte epitopes of the major outer membrane protein of chlamydia trachomatis

ABSTRACT

Disclosed herein are 9 amino acid-long peptides from the major outer membrane protein (MOMP) of Chlamydia trachomatis serovar E. These peptides activate CD8+ cytotoxic T-lymphocytes in human infections that are potentially important for resolution of infection and protection against disease. Thus, the peptides, as well as DNA coding for them, are intended for use in vaccination of humans. Also, they are useful in connection with diagnostic tests.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. Ser. No. 09/314,742 filed May 19,1999.

This invention was made with United States government support awarded bythe following agency: NIH A134617. The United States has certain rightsin this invention.

BACKGROUND OF THE INVENTION

The present invention relates to nine amino acid-long peptides of themajor outer membrane protein (“MOMP”) from Chlamydia trachomatis (“Ct”).These peptides activate human cytotoxic T-lymphocytes (“CTLs”).

Ct is an intracellular bacterium that is the leading cause ofpreventable infectious blindness (ocular trachoma) in the developingworld and of sexually transmitted disease (“STD”) in the United Statesand certain other parts of the developed world. The estimated annualincidence of Ct-caused STD is in the millions. While most Ct-causeddisease can be treated with antibiotics, untreated or inadequatelytreated infections result in hundreds of thousands of cases of pelvicinflammatory disease each year in the United States, alone.

Adverse outcomes of pregnancy, ectopic pregnancy and tubal infertilityare among the consequences of genital tract infections with Ct.Moreover, apparent clearance of infection by a given serovar(serologically distinct strain of Ct) can be followed by the infectionbecoming latent and prolonged or by re-infection. This is importantbecause much Ct-caused pathology results from tissue-damaginginflammatory responses of the immune system that are triggered byrepeated or prolonged exposures to the whole organism. Therefore, thereis a need for improved means to prevent primary infections.

A great deal of effort has been put into developing a vaccine againstdiseases caused by Ct infections. While whole inactivated organisms areoften used as a vaccine to immunize humans, such a vaccine is notdesirable in the case of Ct because certain proteins expressed by Ct,such as chlamydial heat shock proteins, induce pathological immuneresponses rather than protective immune responses and, thus, contributeto disease. As a result, much vaccine-related activity in chlamydialresearch is centered on developing a “subunit vaccine” that consistsonly of Ct protein antigens or specific parts of the proteins thatelicit protective immune responses in vaccinees. The fact that B-cellresponses (neutralizing antibody) to Ct MOMP protect mice from Ct-causeddisease has led to a prevailing theory that MOMP, when used to vaccinatehumans, might also induce protective B- and T-cell responses.

However, using whole MOMP as a vaccine is not a good solution. WholeMOMP is too difficult to isolate from natural Ct cultures in largequantities that are sufficiently pure for use in mass vaccination.Larger quantities of recombinant MOMP could theoretically be produced inE. coli, but the chemical properties (e.g. insolubility except indetergents) impede its large scale preparation as a non-toxic vaccine.Furthermore, use of whole MOMP has too much risk of adverse sideeffects.

Consequently, emphasis has been given to developing a subunit vaccinethat contains multiple B- and T-cell “epitopes” in MOMP, i.e. shortantigenic MOMP peptides that are recognized by B and T cells. To achievethat goal, it is critical to identify which MOMP peptides are recognizedby B and T cells of infected people. To date, there have been a numberof reports regarding attempts to develop vaccines based on single ormultiple MOMP peptide fragments, where the focus is on raising Th—celland/or B-cell responses (mostly in mice, but in some cases, in humans).See H. Su et al., 172 J. Exp. Med. 203-212 (1990) (serovar A); J. Allenet al., 147 J. Immunol. 674-679 (1991) (serovar B); M. Ishizaki et al.,60 Infect. & Immun. 3714-3718 (1992) (serovars B, C); G. Zhong et al.,151 J. Immunol. 3728-3736 (1993) (serovar B). L. Ortiz et al. 157 J.Immunol. 4554-4567 (1996)(serovar E) and U.S. Pat. No. 6,001,372(serovar E). The disclosure of these publications and of all otherpublications referred to herein are incorporated by reference as iffully set forth herein.

The 371 amino acid sequence of mature MOMP of Ct serovar E, a commoncause of genital tract infections, is also disclosed in L. Ortiz et al.157 J. Immunol. 4554-4567 (1996). The naturally occurring DNA codingsequence of serovar E-MOMP is disclosed in E. Peterson et al., 18 Nuc.Acids. Res. 3414 (1990). MOMP is a transmembrane protein and comprisesmore than 60% of all outer membrane proteins of Ct.

Sequence analysis of MOMP from various sources has revealed thatdifferences in amino acid sequence confined to surface-exposed “variablesegments” (VSs) of MOMP account for the serological specificity ofdifferent serovars and, also, for differences in Th-cell responses todifferent isolates. See M. Ishizaki et al., 60 Infect. & Immun.3714-3718 (1992). On the other hand, membrane-embedded regions of MOMPcontain amino acid sequences that are conserved among different Ctserovars, and hence the name, “constant segments (CSs)”. Notably, amajority of Th-cell epitopes is located in MOMP CSs in contrast toB-cell epitopes, which are exclusively located in MOMP VSs.

T cells recognize their peptide epitopes only when they are presented onthe surface of other cells in association with a particular kind of HLA(human leukocyte antigen; human MHC (major histocompatibility complex))molecules. Different kinds of HLA molecules present different peptideepitopes. A complicating matter in vaccination of humans is the factthat HLA genes are extremely polymorphic in the human population. Thatis, different individuals express different HLA types, and a T-cellepitope that elicits immune responses in some individuals may not do soin others. This is a particularly troubling problem for those seeking todevelop vaccines for the human population in general. Consequently,there remains a need to identify many different peptide epitopespresented by diverse HLA allotypes that elicit immune responses in themajority of population. Such a set of epitopes can then be used tocreate a “cocktail” type sub-unit vaccine containing multiple T-cellepitopes as well as B-cell epitopes.

Recently there has been a description in M. Holland et al., 107 Clin.Exp. Immunol. 44-49 (1997) of two MOMP peptides that stimulated limitedCTL responses in HLA-B8+ or HLA-B35+ individuals who had experiencedtrachoma, an eye infection with Ct. However, only two of twelve HLA-B8+subjects responded to the peptide therefor, and only one of thirteenHLA-B35+ subjects responded to the peptide therefor. These CTLs showedlow lytic activity against targets incubated with the peptides andability of the CTLs to lyse Ct-infected target cells was not examined.

Apart from vaccine utility, it is desirable to find CTL epitopes thatcan be used as components of diagnostic tests (e.g. to confirm thepresence of the disease once a positive test result has been obtainedusing conventional tests).

In summary, the identification of human CTL epitopes is needed to designa sub-unit vaccine, and is of interest in developing diagnostic tests.

BRIEF SUMMARY OF THE INVENTION

Our invention concerns a specific type of T cell responses, i.e.cytotoxic T lymphocyte (CTL) responses, in human genital tractinfections with Ct. CTLs have been well documented as critical playersin providing protection against infections with intracellular pathogens,including viruses, bacteria, fungi and parasites. CTLs exert theirprotective effector function by specifically recognizing an infectedcell and secreting cytotoxic molecules that lead to the lysis and deathof the infected cell, as well as the pathogens residing inside the cell.CTL recognition of an infected cell requires presentation on the cellsurface of short peptide epitopes derived from proteins of the pathogensin association with HLA class I molecules.

Such peptides are generated by “the antigen processing machinery” of theinfected cell, which includes cytosolic proteases and the transportermolecules that move the peptides into a cellular compartment where theycan bind to HLA class I molecules. It should be noted that only afraction of peptides generated by a cell are indeed capable ofactivating CTLs. This is because each CTL expresses at the cell surfaceT-cell receptors that are specific for a single kind of HLA classI-peptide complex. It is only when the T-cell receptors bind to correctHLA class I-peptide complexes displayed by an infected cell that theCTLs become activated and capable of killing the infected cell.

In one aspect the invention provides a peptide of 9 to 10 amino acidsequences comprising an amino acid sequence selected from the groupconsisting of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4,SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

In another aspect, the invention provides nucleotide sequences forexpressing such peptides. Such nucleotide sequences are, for example,preferably those that incorporate the applicable coding portion for thefragment of the natural MOMP gene, as described in E. Peterson et al.,18 Nuc. Acids. Res. 3414 (1990). Alternative codons that express thesame amino acids may also be used.

In yet another form, the invention discloses vaccine candidatescontaining such peptides or nucleotide sequences. The vaccines aredesigned to induce cytotoxic T lymphocyte (“CTL”) responses in humans soas to increase the capacity of humans to resist adverse diseasesresulting from Chlamydia trachomatis (“Ct”) infection.

As noted above, activation of CTLs requires specific recognition ofpathogen-derived short peptides (e.g. nine and ten mers are highlypreferred in our case) which have bound to specific kinds of HLA class Imolecules. Moreover, the CTL epitopes can be used to detect MOMPpeptide-specific CTLs in peripheral blood of infected people and thusprovides a diagnostic tool.

Detection of the MOMP-specific CTLs can be accomplished in two basicways. First, a reagent called a “HLA class I tetramer” incorporating theinvention can be used to enumerate MOMP peptide-specific CTLs in bloodsamples directly upon their removal from subjects being diagnosed forinfection. Second, the CTLs in such blood samples can first be activatedwith our invention to proliferate in vitro and then be enumerated withthe use of tetramers.

If a conventional diagnostic test based on Th-cell or B-cell antigenicresponse provides a negative initial result, false negatives and truepositives can be diagnosed by checking blood samples using directdetection or activation followed by detection of the CTLs as theindicator. Thus, the invention can provide a method for diagnosingwhether a human has been infected with Ct. Moreover, since the numbersof CTLs may reflect the stage of the infection and progress ofpathogenesis, enumeration of the CTLs provides a diagnostic basis forprognosis.

The basic tools are HLA class I tetramers, each kind of tetramerincorporating just one or another of the eight claimed peptides thatcomprise the invention in combination with the specific kind of HLAclass I molecules that binds the peptide. Each kind of tetramer binds toonly those CTLs that recognize and are activated by the peptide used tomake that kind of tetramer. The tetramers are fluorescently tagged in away that allows each cell that binds a tetramer to be counted with adevice called a flow cytometer. Thus, creation of the powerful toolscalled tetramers depends on identifying peptide epitopes that arerecognized by CTLs; the invention identifies eight such epitopes.

The advantages of the present invention therefore include providing:

(a) peptides that can activate human CTLs;

(b) genes coding for such peptides;

(c) sub-unit vaccines based on such peptides; and

(d) diagnostic tests using such materials.

These and still other advantages of the present invention will beapparent from the description which follows. The following descriptionis merely of the preferred embodiments. Thus, the claims should belooked to in order to understand the full scope of the invention.

DETAILED DESCRIPTION General Overview

We have discovered that HLA class I-restricted CD8⁺ CTLs specific forthe Ct MOMP are present in the peripheral blood of humans who acquiredgenital tract infections with the organism. Three HLA-A2-restrictedepitopes, two HLA-B51-restricted epitopes, one HLA-B62-restrictedepitope, and two HLA-B35 epitopes have been identified in MOMP of Ctserovar E, which is a common cause of genital tract infections. One ofthe eight epitopes spans a variable (non-conserved) segment of MOMP andis likely a serovar E-specific epitope that is recognized only bysubjects infected with serovar E (SEQ ID NO 1). The other seven epitopesare localized in conserved segments (SEQ ID NOs 2-8) and are recognizedby CTLs isolated from all infected subjects tested, regardless of theirinfecting serovars.

The relevance of the CTLs we detected to genital tract infections withCt is attested to in at least three ways. (a) CTLs that recognizepeptides from MOMP of Ct do not respond to peptides derived from thecorresponding peptides of MOMP from the related common human pathogenChlamydia pneumoniae, which causes different diseases. (b) HLA class Itetramers made with claimed peptides bind to significant numbers of CD8+T cells when the cells are derived from Ct-infected subjects but notfrom uninfected subjects. (c) ME180 and HeLa human cervical epithelialcells productively infected with Ct are lysed by MOMP peptide-specificCTLs; uninfected cells are not lysed. These cell lines are the type ofcell that is naturally infected with Ct in the female genital tract andour results indicate that such infected cells could be lysed by theMOMP-specific CTLs in vivo.

Materials And Methods

Human subjects who had recent symptomatic genital tract infections withChlamydia trachomatis (“Ct”) were recruited. All the infected STDsubjects were treated with an oral dose of azithromycin uponconfirmation of Ct infection. HLA-A2⁺ purportedly uninfected controlsubjects were recruited from the similar age group. Control subjects hadbeen sexually active, but lacked previous history of genital tractinfections with Ct.

HLA class I typing was performed by PCR-sequence specific primeramplification, using Class I ABC SSP Unitray kit (Pel-Freez ClinicalSystems, Brown Deer, Wis.).

B lymphoblastoid cell lines (LCLs) were established from human subjectsby transformation of peripheral blood mononuclear cells (“PBMCs”) withEpstein-Barr Virus. HLA class-I mutant cell lines used as targets in CTLassays were derived from LCL 721. Mutants LCL.45 and LCL.19 were derivedby mutagenizing LCL 721 with gamma rays and by using complement plusappropriate antibodies to select for HLA deletion mutants. Both LCLs.45and .19 have the HLA-A2 and -B51 loci.

Further mutagenesis of LCL.45 produced mutant LCL.144, which isHLA-A-null due to a homozygous deletion at the locus; HLA-B51 remainsintact. Similarly, HLA-B-null mutant LCL.53 was derived from LCL.19 as aresult of intragenic deletion at the B locus but retains HLA-A2. LCLswere cultured at 37° C., in humidified 5% CO₂ in '2/1 RPMI′; RPMI 1640(85%) supplemented with fetal calf serum (5%), defined/supplemented calfserum (10%), 25 mM HEPES, 44 mM NaHCO₃, 2 mM L-glutamine, 100 U/mlpenicillin and 100 μg/ml streptomycin sulfate.

ME180 and HeLa human epithelioid carcinoma cells were used as a modelfor female genital tract epithelial cells that support the growth of Ct.ME180 was typed to be HLA-A1, -A32, -B8 and -B44 and HeLa was typed tobe HLA-A3, -A68 and -B70 according to PCR-based typing (Tissue TypingLaboratory, University of Wisconsin, Madison, Wis.). ME180 cells werecultured in MEM containing 10% fetal calf serum, 100 μM non-essentialamino acids, 25 mM HEPES, 44 mM NaHCO₃, 100 U/ml penicillin and 100μg/ml streptomycin sulfate. ME180 cells expressing an HLA-A1(ME180[A1]), HLA-A2 (ME180[A2]), or HLA-B51 transgene (ME180[B51]) wereprepared by introducing into ME180 cells the RSV.5neo vector carryingthe genomic HLA-A*0101, HLA-A*0201, or HLA-B51*01 gene, respectively.Stable transferent cells were selected for resistance to G-418 sulfate(500 μg/ml). The transferent cell lines permitted studies of CTLsspecific for HLA class I molecules that were not initially present inthe epithelial cells.

Human T cells were grown at 37° C. in humidified 5% CO₂ using DMEMcontaining 4.5 g/L glucose and supplemented with 10% pooled AB-negativehuman serum, 100 μM non-essential amino acids, 25 mM HEPES, 44 mMNaHCO₃, 2 mM L-glutamine, 100 U/ml penicillin and 100 μg/ml streptomycinsulfate. When needed, recombinant human IL-2 (rhIL-2) was added at 25U/ml. Human serum was purchased from Pel Freez (Brown Deer, Wis.), andbovine sera were purchased from Hyclone Laboratories (Logan, Utah). Alltissue culture media and reagents were purchased from Gibco-BRL (GrandIsland, N.Y.). All other chemicals were purchased from Sigma (St. Louis,Mo.).

Peptide Synthesis

Nine-mer peptides in accordance with SEQ ID NOs: 1-8 possessing “bindingmotifs” (amino acid residues at the second and ninth positions that arerequired for peptide binding to HLA class I) for HLA-A2 (or HLA-B51 orHLA-B62 or HLA-B35) were identified in the mature Ct serovar-E MOMPsequence. C. pneumoniae MOMP peptides were made according to thepublished amino acid sequences.

Peptides were synthesized at the University of Wisconsin BiotechnologyCenter (Madison, Wis.) by F-moc chemistry. Identities of peptides wereconfirmed by amino acid analysis and matrix-assisted laserdesorption/ionization mass spectrometry. Lyophilized peptides weredissolved in DMSO at 20 mM, aliquotted and stored at −80° C. Peptideswere diluted to 4 mM with serum-free culture medium and used at desiredfinal concentrations.

Ct MOMP peptides that can bind to HLA-A2 molecules were identified bytheir ability to increase the expression of HLA-A2 on the surface ofTAP-deficient mutant cell line LCL.174. Briefly, LCL.174 was plated in around-bottomed 96-well plate at 200,000 cells/well in 200 μl of 2/1 RPMItogether with 50 μM of peptide and incubated overnight at 37° C. Thecells were then stained with HLA-A2-specific monoclonal antibody, BB7.2(ATCC, Rockville, Md.), followed by fluorochrome (“FITC”)-conjugatedgoat anti-mouse IgG. Fluorescence intensity was analyzed by flowcytometry. Influenza virus matrix M1 protein peptide, FluMP58, is aknown HLA-A2-presented CTL epitope and used as a positive control.Hepatitis B virus envelope antigen peptide, HBenvAg125, does not bind toHLA-A2 and was used as a negative control.

Stimulation Of CTLs

PBMCs were prepared from ˜30 ml of heparinized peripheral blood obtainedfrom human subjects by centrifugation over Ficoll-Hypaque (Sigma, St.Louis, Mo.). CD8⁺ cells were positively selected from freshly isolatedPBMCs, or sometimes from PBMCs frozen in liquid N₂, using anti-CD8magnetic microbeads according to the manufacturer's instructions(Milteny Biotec, Auburn, Calif.).

Negatively selected cells were resuspended in serum-free DMEM and platedin 500 μl aliquots into 48 well plates at 3×10⁶ cells/well. After 2 hrat 37° C., 5% CO₂, non-adherent cells were removed by repeated washing,and adherent monocytes were incubated for 4 hr with 50 μM peptide and 5μg/ml human β-2-microglobulin (Sigma, St. Louis, Mo.). After beingwashed with serum-free DMEM, each well received 1.5×10⁶ CD8⁺ cells (>95%pure by flow cytometry) in 500 μl of DMEM containing 10% human serumsupplemented with rhIL-7 (0.5 ng/ml; R&D Systems, Minneapolis, Minn.).

rhIL-2 was given at 25 U/ml after 2 days and twice a week thereafter byreplacing half of the culture medium. On day 10, CTL cultures wererestimulated at a responder to stimulator ratio of 5 with irradiated(5000 rad), autologous LCLs incubated with 20 μM peptide. Alternatively,LCL.174 incubated with 50 μM peptide was used to restimulate CTLcultures obtained from HLA-A2⁺ subjects. CTL assays were performed aweek after restimulation as described below.

After initial characterization, peptide-stimulated CTLs could be frozenin medium that consisted of 30% human serum, 10% DMSO and 60% DMEM, andthen thawed and restimulated for further analysis. Influenza virusmatrix M1 protein peptide, FluMP58, was used as a positive control forin vitro stimulation of peptide-specific CTLs.

CTL Assays

Cytolytic activity of peptide-stimulated CTL cultures was assessed in[³H]thymidine release assays or in [³H]uridine release assays. TargetLCLs (3×10⁵ cells/ml) were labeled overnight with [³H]thymidine (2.0Ci/mmol; New England Nuclear, Boston, Mass.) or with [³H]uridine (25˜30Ci/mmol; Amersham, Arlington Heights, Ill.) at 10 μCi/ml, while ingrowth phase. After 1 hr incubation with or without 10 μM peptide, thetarget cells were washed three times to remove excess peptides. 5000target cells were then plated in round-bottomed wells of 96-well platesalong with different numbers of CTLs in a total volume of 200 μl of 2/1RPMI to give desired effector (CTLs) to target ratios.

After 6 hr at 37° C., 100 μl of supernatant was harvested from eachwell, air-dried on glass fiber filters and counted in a liquidscintillation counter. Spontaneous release was determined for targetcells in the absence of CTLs in medium alone. Maximal labeling wasdetermined from equivalent wells by taking 100 μl after thoroughlymixing the contents of the wells. Maximal labeling was 3000-5000 cpm for[³H]thymidine-labeled LCLs, and 6000-8000 cpm for [³H]uridine-labeledLCLs. Spontaneous release was typically 5-10% of maximal labeling. WhenME180 cells were used as targets, adherent cells were incubatedovernight with radioactive labels as described above. Cells were thentrypsinized and incubated for 1 hr with or without 10 μM peptide beforebeing plated together with CTLs.

Maximal labeling was 5000-6000 cpm for [³H]thymidine-labeled ME180cells, and ˜10,000 cpm for [³H]uridine-labeled ME180 cells. Spontaneousrelease was usually 5-10% of maximal labeling.

Chlamydia-Infected Target Cells

Serovar E/UW-5 genital strain of Ct was grown in HeLa cells and purifiedby density gradient centrifugation. See generally our article at S. Kimet al., 162 J. Immunol. 6855-6866 (1999) (not prior art). The purifiedelementary bodies (EBs) were resuspended in SPG(sucrose-phosphate-glutamic acid buffer) and stored at −80° C. untiluse. Inclusion forming units (IFUs) of purified organisms were assayedon HeLa cells by indirect fluorescent-antibody staining as previouslydescribed.

ME180 and ME180[A2] cells were maintained without antibiotics until theywere inoculated with Ct. Cells were seeded at 3×10⁵ cells/well in a12-well plate (Costar, New York, N.Y.) together with 10 μCi/ml[³H]uridine. A 24-hour subconfluent monolayer was washed twice with PBSand inoculated with live, heat-killed or UV-killed EBs at a multiplicityof infection (MOI) of 10 (i.e. 10 IFUs per cell) in 500 μl of serum-freeRPMI for 2 hr at 37° C. Heat-killed EBs were prepared by incubating themin a 56° C. water bath for 30 min, and UV light-inactivated EBs byexposing the organisms to a 30 W UV source (10 erg/sec, GeneralElectric, Fairfield, Conn.) at a distance of 10 cm for 30 min.

Live EBs and killed EBs were used at equal dilutions. Inocula wereremoved by washing, and infected cells were cultured for 24 hr or for 48hr in antibiotic-free RPMI 1640 containing 10% fetal calf serum beforeuse in CTL assays. Uninfected cells were treated with medium alone,incubated for the same amount of time and used as a control in CTLassays.

CTL assays were performed with 5000 infected cells per well at aneffector-to-target ratio of 50, as described above. Spontaneous releasefrom infected cells was ˜10% of maximum labeling at 24 hr post-infectionand 15-20% at 48 hr post-infection; lysis of infected cells by CTLs wasmeasured at these time points. At 72 hr post-infection, 60-70% ofinfected cells spontaneously lysed; this time point and later ones wereexcluded from our experiments. Spontaneous release from cells incubatedwith killed organisms remained similar (˜10% of maximal labeling) up to96 hr post-inoculation.

RESULTS

We chose to examine Ct MOMP-specific CTL responses restricted by HLA-A2,HLA-B51, HLA-B62, and HLA-B35, which are among the most common HLA classI allotypes found in various ethnic populations. Out of twenty-oneCt-infected subjects who enrolled in our research program, 14 (67%) weretyped to be HLA-A2⁺; 4 (20%) were typed to be HLA-B51⁺; 5 (24%) weretyped to be HLA-B62⁺; and 3(14%) were typed to be BLA-B35+. All of thesubjects yielded CTLs that responded to one or more MOMP peptides usedto stimulate outgrowth of the CTLs in vitro. This, the peptidescomprising our invention have the valuable attribute as vaccinecomponents of eliciting CTL responses in at least a large proportion ofinfected subjects who have the kinds of HLA molecules that present thepeptides to the immune system.

In making these determinations, amino acid sequences containing “bindingmotifs” for these HLA class I allotypes were identified in MOMP of Ctserovar E and were then synthesized and used to stimulate outgrowth ofCD8⁺ T cells obtained from peripheral blood of Ct-infected humansubjects. Serovar E was chosen for the study, because it is one of themost common causes of human genital tract infections.

A total of 14 MOMP peptides possessing a proposed HLA-A2-binding motifwere tested for their ability to bind to HLA-A2 molecules.

SEQ ID NOs: 1, 2 and 3 were identified as binders of HLA-A2 by means ofbinding studies with LCL.174 and were subsequently used for in vitrostimulation of CD8⁺ cells obtained from HLA-A2⁺ subjects. SEQ ID NO: 1is an HLA-A2-presented CTL epitope that spans a variable segment of MOMPand is recognized only by subjects infected with serovar E. Thus, thisepitope is most likely a serovar E-specific epitope. However, SEQ IDNOs: 2 and 3 are located in the constant segments of MOMP and arerecognized by CTLs isolated from all 14 HLA-A2+ infected subjectstested, regardless of their infecting serovars.

Four synthetic peptides possessing binding motif for HLA-B51 were usedin stimulation of CD8⁺ cells from HLA-B51⁺ subjects without performingpreliminary peptide binding assays. Two of them, SEQ ID NOs: 4 and 5were found to activate CTLs in HLA-B51+ STD subjects.

Similar experiments were performed with two peptides containing abinding motif for HLA-B62. One of the peptides, SEQ ID NO: 6, wasrecognized by three HLA-B62 subjects tested.

Similar experiments were performed with two peptides containing abinding motif for HLA-B35. Both peptides, SEQ ID NOs: 7 and 8, wererecognized by two HLA-B62+ STD subjects tested.

To confirm that the MOMP peptide-specific CTLs described above wereindeed elicited by genital tract infections with Ct, HLA-A2⁺ uninfectedsubjects were recruited based on the lack of previous history of Ctgenital tract infections. Their peripheral blood CD8⁺ T cells wereexposed in vitro to peptides SEQ ID NOs: 2 and 3 following the sameprotocol used for infected subjects. The cytolytic activity of CTLcultures was assessed in [³H]thymidine release and [³H]uridine releaseassays performed in parallel, using HLA-A2⁺ LCL.53 as targets.

Five of six uninfected control subjects had no detectable CTL activityagainst the two MOMP peptides, while one had CTL populations specificfor both peptides. The basic CTL stimulation protocol was functional inthis experiment, as we detected influenza peptide-specific CTLs in allsix control subjects. The MOMP-specific CTLs found in one of our controlsubjects may reflect previous asymptomatic infection with CT, whichcommonly occurs. Thus, it is noteworthy that asymptomatic Ct infectioncan be diagnosed in a seemingly uninfected person by in vitrostimulation of T cells with our inventions.

An additional control subject (HLA-A2+ and HLA-B51+) was tested withHLA-B51-restricted CTL epitopes, SEQ ID NOs: 4 and 5, as well as withHLA-A2-restricted CTL epitopes SEQ ID NOs: 2 and 3. None of thesepeptides stimulated CTLs in this subject.

We also addressed the possibility that the MOMP-specific CTLs we weredetecting had actually been elicited by prior infection of our STDsubjects with Chlamydia pneumoniae (Cpn). It was important to do thisbecause immunological cross-reactivity of Ct MOMP and Cpn MOMP couldconfound the use of our invention as components of vaccines and asdiagnostic tools. This was particularly important for CTL epitopeslocated in constant segments of MOMP, where Ct MOMP and Cpn MOMP sharemore than 70% sequence homology. Therefore, peptides of Cpn MOMP thatcorrespond to our inventions (Ct MOMP CTL epitopes SEQ ID NOs: 2-5) weresynthesized and CTL assays were performed with them. We found that whenCTLs were elicited with given Ct MOMP peptides, target cells exposed tothe same Ct MOMP peptides were lysed by the CTLs but the CTLs did notlyse the same target cells exposed to the corresponding Cpn peptides.Thus, the CTLs we detected in STD subjects are not cross-reacting CTLsthat have resulted from Cpn infections but are specific for genitaltract infections with Ct.

In order to show that the CTLs detected and elicited with our inventioncould actually interact with infected cells in vivo, we determinedwhether the CTLs could lyse human female genital tract epithelial cellsthat presented appropriate MOMP peptides. This demonstration was made inthree stages. First, we exposed PBMCs from HLA-A2+ and -B51+ Ct-infectedSTD subjects to peptides SEQ ID NOs: 2 and 3 and to peptides SEQ ID NOs:4 and 5, respectively, to elicit outgrowth of peptide-specific CTLs. TheCTLs elicited by these peptides were first shown to lyse LCL targetsonly in the presence of the peptide used to elicit their outgrowth andonly if the cells expressed HLA class I molecules to which the peptidesbound. Using such proven CTLs, it was then shown that ME180 humancervical epithelial cells behaved just as did the LCLs. The CTLs lysedME180 targets only if the peptide used to stimulated the outgrowth ofthe CTLs was present and only if the ME180 targets expressed the HLAclass I molecules to which the peptides bound.

The final demonstration was to show that the CTLs grown out bystimulation with our invention could destroy (i.e. lyse) genital tractepithelial cells actually infected with Ct. For this purpose, we usedCTLs that had been elicited by in vitro stimulation with withHLA-A2-presented CTL epitopes (SEQ ID NOs: 2 and 3). ME180 or itsHLA-A2-expressing transferent cells were labeled with [³H]uridine,infected with Ct and used as targets for the CTLs. The infected targetswere lysed only if they expressed HLA-A2; uninfected cells were notlysed even if they expressed HLA-A2.

In summary, the peptides comprising our invention detect and elicit theoutgrowth of CTLs that lyse Ct-infected human genital tract epithelialcells and could well play an important role in clearing Ct infection invivo.

Diagnostic Protocols

It will be appreciated that instead of using known blood samples,samples from subjects whose infection status is not known can be testedvia the above techniques. An example protocol for a diagnostic test isas follows.

The ability to detect MOMP peptide-specific CTLs is in a human subjectindicates that a previous infection with Ct or an immunization, e.g.with a MOMP-based vaccine, was able to induce CTL responses in thatperson.

Once one knows HLA class I-presented peptide epitopes specificallyrecognized by CTLs, an extremely sensitive and specific method to detectpeptide-specific CTLs is available, thanks to the development of HLAclass I tetramers as described in J. Altman et al., 274 Science 94-96(1996). Tetramers are soluble reagents formed by four identical HLAclass I molecules folded in vitro with a synthetic peptide thatcorresponds to a CTL epitope presented by the specific kind of HLA classI molecule comprising the tetramer.

Tetramers have become a popular reagent for detecting antigen-specific Tcells isolated from a variety of sources. By attaching a fluorescentmarker to the tetramers, T cells that specifically recognize the peptideused for tetramer folding can easily be detected by flow cytometry.

The MOMP CTL epitopes we identified can be used to create such HLA classI tetramers, for use in diagnostic tests. For example, we have madeHLA-A2 tetramers folded with two of the claimed sequences (SEQ ID NOs: 2and 3) and successfully used the reagents to detect MOMP CTLs in theperipheral blood of Ct-infected people. This also confirmed ourinteresting novel finding that CTLs specific for our sequences indeedexist in vivo.

CD8+ cells of HLA-A2+ STD subjects were stimulated in vitro with thepeptides SEQ ID NOs: 2 and 3 and stained with tetramers at indicatedtime points. Staining is specific. T cells cultures stimulated with thetwo peptides were stained by the corresponding tetramers. T cells thatwere stimulated with HLA-B62-presented epitope (SEQ ID NOs: 6) were notstained by either of these tetramers.

Tetramers can detect CTLs present at a very low frequency in freshperipheral blood and one does not have to do in vitro stimulation to beable to detect such CTLs. Despite the low frequencies oftetramer-binding T cells in freshly drawn blood samples, we have studiedmultiple HLA-A2⁺ infected subjects and found that these low frequencieswere always higher than the “background” frequencies of T cells thatbind the A2 tetramers in HLA-A2⁻ infected subjects or in uninfectedHLA-A2⁺ subjects.

Ct genital tract infections can follow different courses and havepathological sequelae that differ in severity among infectedindividuals. Tetramers made with the peptides comprising our inventions(SEQ ID NOs: 1-8) will be valuable tools for monitoring the numbers ofMOMP-specific CTLs in various body locations, e.g. peripheral blood andgenital tract epithelial cells. Such diagnostic determinations made withthe invention will provide valuable information that could not beobtained so readily by other means concerning the relations between CTLnumbers and locations, on the one hand, and clearance of infections orpathogenesis, on the other. HLA class I tetramers formed with MOMP CTLepitopes will also be valuable for monitoring the outcome of thevaccination described below, i.e. to determine whether the vaccinationhas indeed worked and induced Ct.-specific immune responses. If thevaccine has worked, one should be able to use tetramers to detectincreasing frequencies of MOMP CTLs following immunization.

Vaccine Protocol-A

In a sterile dropper bottle, the suspending medium is sterilephosphate-buffered saline. Some or all of SEQ ID NOs: 1-8 is present at4 mg/ml. Cholera toxin subunit B at 2 mg/ml is also present to enhanceimmune responses at mucosal surfaces, which are the sites at which Ctmultiply and cause pathology. Use of subunit B has been safely testedwith humans in other contexts.

To administer to a human, one shakes well, and uses two drops (about 0.1ml) in each nostril and each eye. Administration should preferably be ondays 0, 7 and 14. T- and/or B- cell epitope peptides may also optionallybe included, as may booster applications.

Vaccine Protocol-B

The proposed vaccine agent is an attenuated bacterial strain ofSalmonella typhimurium bearing a replicating plasmid into which isinserted DNA sequences capable of expressing the peptides of interest invivo. We propose as a vector attenuated Salmonella typhimurium strain_(xo)4072. See F. Schödel et al., 62 Infect. and Immun. 1669-1676 (1994)which has A crp-1 and Δ cya mutations that render it avirulent and a ΔasdA-1 mutation that renders it inviable unless a normal asdA gene ispresent on an indwelling plasmid.

Plasmid PYAN is a form of pYA292 that is modified to have a Nco I site.See Schodel et al., supra. The presence of the Nco I site allows inframe insertion of the AUG of the foreign protein of interest into theplasmid. PYAN lacks antibiotic resistance genes, allowing use ofantibiotics should symptoms suggestive of Salmonella pathology appear.

pYAN does have a normal asdA gene, which maintains viability of onlythose bacteria that retain the plasmid. A DNA sequence is synthesizedencoding an AUG followed by the sequences encoding the peptide. Thesuggested dose is 5×10⁴ colony forming units for small children and5×10⁵ colony forming units for adults.

For adults, the bacteria will be administered with sodium bicarbonate (2g of NaHCO₃ in 150 ml of distilled water). One should first drink 120 mlof the solution to neutralize gastric acid. One minute later, one drinksthe remaining 30 ml of bicarbonate solution, now containing thebacteria. No food or drink is permitted for 90 minutes before or aftervaccination.

Vaccine Protocol-C

Alternatively, the DNA may be delivered by other DNA delivery techniquese.g. with a “gene gun” in which the DNA is adsorbed to microscopic goldparticles that are propelled into skin cells of vaccinees by a pulse ofhigh pressure helium. The invention has three features that make itespecially suitable for use in DNA vaccines.

(1) MOMP peptide 249-268 contains five known human CTL epitopes and sixknown T helper cell epitopes; this 20-mer has the highest density ofhuman T cell epitopes that has been reported for any antigen. Thus,quite a short segment of DNA can elicit CTL responses to multiple CTLepitopes.

(2) Our CTL epitopes overlap T helper cell (Th) epitopes. Th cellssecrete various cytokines, which facilitate the generation and long-termmaintenance of CTL responses. Indeed, accumulating experience with DNAvaccines, including some delivered with the gene gun, indicates that CTLresponses are enhanced when the vaccine DNA encodes Th cell epitope(s).This juxtaposition of the two kinds of epitopes is observed with alleight of our CTL epitopes. It exists for epitopes located in MOMPsegment 249-268, but note also that the isolated CTL epitopes SEQ IDNOs. 1, 4 and 5 overlap Th epitopes that are located in peptides 89-105,157-175 and 344-359, respectively. Thus, DNA segments encoding each ofour CTL epitopes would also encode Th epitopes, increasing the chancesthat responses to the CTL epitopes would be enhanced by the Th epitopes.

(3) Our CTL epitopes in aggregate are presented with four differentkinds of HLA class I molecules (HLA-A2, -B35, -B51 and -B62). Thus,their use as vaccine components should elicit immune responses to one ormore CTL epitopes in a large proportion of the population. Thisversatility of the vaccine is increased by the fact that diverse HLAclass II (DR) molecules present to the immune system the Th epitopesthat overlap the CTL epitopes. This increases the chance that the CTLresponses will be enhanced by the Th responses elicited by the same DNAfragment.

In all three respects set out above, our invention is unique with regardto human CTL epitopes in Ct MOMP.

While the preferred embodiments have been described above, it will beappreciated by those skilled in the art that other modification can bemade within the scope of the invention. For example, instead ofexpressing the DNA in E. coli, one might optimize the DNA for otherhosts and express it in those hosts.

Further, while six specific sequences have been identified, it isbelieved that the techniques of the present invention can be utilized toidentify other desired 8-10 mers having desirable CTL activationcharacteristics. Thus, the claims should be looked to in order to judgethe full scope of the invention.

Industrial Applicability

The invention provides peptides and DNA that can be used for diagnosticand vaccination purposes.

                   #             SEQUENCE LISTING<160> NUMBER OF SEQ ID NOS: 8 <210> SEQ ID NO: 1 <211> LENGTH: 9<212> TYPE: PRT <213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 1Ser Leu Asp Gln Ser Val Val Glu Leu   1               5<210> SEQ ID NO: 2 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 2Arg Leu Asn Met Phe Thr Pro Tyr Ile   1               5<210> SEQ ID NO: 3 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 3Asn Met Phe Thr Pro Tyr Ile Gly Val   1               5<210> SEQ ID NO: 4 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 4Asn Ala Ala Cys Met Ala Leu Asn Ile   1               5<210> SEQ ID NO: 5 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 5Asp Ala Asp Lys Tyr Ala Val Thr Val   1               5<210> SEQ ID NO: 6 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 6Trp Gln Ala Ser Leu Ala Leu Ser Tyr   1               5<210> SEQ ID NO: 7 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 7Ala Ser Leu Ala Leu Ser Tyr Arg Leu   1               5<210> SEQ ID NO: 8 <211> LENGTH: 9 <212> TYPE: PRT<213> ORGANISM: Chlamydia trachomatis <400> SEQUENCE: 8Leu Ala Leu Ser Tyr Arg Leu Asn Met   1               5

We claim:
 1. A purified peptide of 9 to 10 amino acid residues thatactivates cytotoxic T-lymphocytes, the pelptide comprising an amino acidsequence of SEQ ID NO: 7, wherein the peptide does not have more than 10amino acid residues.
 2. A purified peptide of 9 to 10 amino acidresidues that activates cytotoxic T-lymphocytes, the peptide comprisingan amino acid sequence of SEO ID NO: 8, wherein the peptide does nothave more than 10 amino acid residues.